Hissing and Hum through speakers

Hi everyone,
I have a fair amount of hissing and small hum coming through my speakers...when music is played at mid to high volumes the hissing and distortion is very audible through the tweeters/speakers. I don't think it is distortion (not sure how I can tell) I think it is that noise that exists in the system and it gets exaggerated at higher volumes...

I have a Panamax unit where everything is plugged in and the Panamax and amplifier plug in to the same wall outlet.

The noise goes away when I mute my pre-amp (Meridian 561.) But with the pre-amp on and non-muted and any source selected the noise is present. Even when the source is in pause.

Also, I have unplugged the inputs from the pre to the amp (line level) and the noise is still present. Same for my center channel amp, and I also have a third amp with same results..

Does this indicate that the noise is coming from my AC line? I have done most of the troubleshooting (different cables, plugging and unplugging sources, et cetera) that I know and have not been able to resolve...
Can you borrow a different preamp to see if its the preamp?

If one of your sources has a volume control or level attenuater you could bypass the preamp and see if that is the problem.

Another cause could be a ground loop. Try lifting the ground on the preamp with a cheater plug. If that doesnt work try it on the amps also. Some people recomend lifting all grounds. That may be an electrical shock hazard though.

Good luck
Do you have a Plasma/LCD TV also plugged into the outlet or on the same electrical line?
thanks for your responses..

I have moved the Plasma to another circuit. I do have a cable box in the rack, but plugging and unplugging the power of the box as well as the coaxial from the wall, made no difference.

I have tried a different preamp and I get the same results.

The preamp (Meridian 561) has a 3-prone cord and it is plugged in to the Panamax conditioner. So are the rest of the sources. The Panamax is plugged in to one plug on a duplex outlet and the Amplifier for the fronts is plugged in to the other plug of the same outlet.

Also, there possibly seems to be some level matching issues with the 561 (45 Ohms output impedance) and the amp (23.5K ohms input impedance on the rca inputs.) I tried to reduce the gain on the front L/R outputs of the 561 (via the software) from 0db to -2 db, and I think it made a slight difference with the hissing/distortion at high levels, not sure yet...

Not sure what it means exactly...I think if I keep reducing it more I will run out of gain (enough SPL) out of my amp soon, which is weird as it is suppose to be putting out 250W at 8 ohms (so around 330W with my 6 ohm speakers?)
Is it possible that the panamax is the culprit?
that is one of their best pieces but good suggestion...

I will just plug in the CD player in the Meridian and then have the CD, the Meridian, and the amp going to the wall directly and see what the results are..

thank you
thinking about for one more second, I doubt it...with nothing plugged in to the inputs of the amp, and just the speakers plugged in to the amp, I still get the same noise and hum...I will try it anyway..
What speakers are you using and how sensitive are they?

If they are close to 100db then you may need a quieter amp.
they are the Jamo C809, 89db...6 ohms..

I plugged my ipod in directly to the amp just for the heck of it (headphone out so that I can adjust the volume,) and it seems like the slight hum that I had went way down, but the hissing sound from the tweeters is definetelly there...

Not sure it is the amp, I think it is AC line noise but wouldn't that be more in the form of a hum instead of hissing tweeter sound?

Thanks guys...
The hum is probably a ground loop. I don't think the hiss is AC related.

You might try a different set of speakers to see if your still getting the hiss. Are the speakers new?

The reason the hum went down with the ipod is because it runs on a battery and isn't causing a ground loop. PS audio sells power cords that have a removable ground pin. Do a search on ground loops you'll find lots of info on them because they are a common problem.

You've eliminated the preamp and source as the problem so its got to be the amp or speakers. Since you've tried different amps that leaves the speakers.
You might try plugging the whole system into another circuit to see if that changes anything.
I don't think that your results with nothing connected to the amp are meaningful, unless you connect shorting plugs to the inputs (which will probably kill both the hiss and the hum, especially given that you initially reported that the noise went away when you had the preamp connected and muted).

As an experiment, I'd suggest connecting the preamp to the amp, a source component to the preamp, and the ac cords of ALL of these components either to the Panamax (if it can handle the current requirements), or else to the wall without the Panamax. That will eliminate the possibility that some or all of your problem is caused by voltage differentials between the grounds/chassis of the different components.

Not sure what you meant by "there possibly seems to be some level matching issues with the 561 (45 Ohms output impedance) and the amp (23.5K ohms input impedance on the rca inputs.)" Ideally preamp output impedance should be as low as possible, and power amp input impedance as high as possible. Those numbers sound fine, although the amp's input impedance is probably lower than typical, which might result in signal loss if the preamp output impedance were unusually high (which it is not).

-- Al
Also, you mentioned that you moved the plasma to another circuit. Did you also try unplugging it? If it is physically close, it's possible that it is radiating high frequency interference into the audio system through the air, regardless of what circuit it is plugged into.

-- Al
Thanks for your response...I did unplug the Plasma...it is also located in a different room than my equipment is (about 20' away from on the other side of the wall.)

I will try the experiment with 1 source, preamp and amp only connected.

Thanks again...